Conventionally, an air-conditioning apparatus, such as a multi-air-conditioning apparatus for a building, is configured such that cooling operation or heating operation is carried out by circulating a refrigerant between an outdoor unit that is a heat source device disposed outdoors and indoor units disposed indoors. Specifically, heating or cooling of a conditioned space is carried out with air that has been heated by the refrigerant rejecting its heat into the air or with air that has been cooled by the refrigerant removing its heat. Regarding the refrigerant used for such an air-conditioning apparatus, a hydrofluorocarbon (HFC) based refrigerant, for example, is typically used. An air-conditioning apparatus using a natural refrigerant, such as carbon dioxide (CO2), has also been proposed.
There is also an air-conditioning apparatus having a different configuration represented by a chiller system. Further, in such an air-conditioning apparatus, cooling or heating is carried out such that cooling energy or heating energy is generated in a heat source device disposed outdoors; a heat medium such as water or brine is heated or cooled in a heat exchanger disposed in an outdoor unit; and the heat medium is conveyed to indoor units, such as a fan coil unit or a panel heater, disposed in the conditioned space (see Patent Literature 1, for example).
Moreover, there has been proposed an air-conditioning apparatus called a heat recovery chiller in which a heat source unit is connected to each indoor unit with four water pipes arranged therebetween, supplies cooled or heated water or the like simultaneously, and allows cooling or heating to be freely selected in the indoor units (see Patent Literature 2, for example).
In addition, there is an air-conditioning apparatus configured such that a heat exchanger for a primary refrigerant and a secondary refrigerant is disposed near each indoor unit and the secondary refrigerant is conveyed to the indoor units (see Patent Literature 3, for example).
Furthermore, there is an air-conditioning apparatus in which an outdoor unit is connected to each branch unit including a heat exchanger with two pipes and in which a secondary refrigerant is conveyed to the corresponding indoor unit (see Patent Literature 4, for example).